Kahn responded to Trump's tweets on Tuesday morning by telling CNN that the American president was acting like an "11 year-old" but that he didn't feel "it's for me to respond in a like manner".
The economic meeting at St. James's Palace brought together 10 leading companies - five from the UK and five from the United States.
A key area of discord between the allies has been Britain's preliminary decision to allow Huawei a restricted role in building parts of its 5G network. The brooch was wrapped inside a custom White House jewelry box. A handful of supporters does not make a quorum of Trump support, of course, but at least there are some Brits there looking out for the commander-in-chief of the United Kingdom's closest ally. "It will be a very fair deal and I think that this is something that your folks want to do, my folks want to do, and we want to do and we're going to get it done".
At their initial visit to the palace early Monday morning, the Trumps had a private lunch with the queen, later inspecting a collection of artifacts including an 18th-century map of NY, historic photos of golf at St. Andrews and books about birds and George Washington.
Impersonator Phil Ball said the US President was "not an ethical person" who would look to take advantage of the United Kingdom in any future trade deal between the two nations post-Brexit.
Although Trump and May did not appear to conclude the "substantial" trade deal that the president said he supports, he did soften the line his administration has taken with London over a thorny security dispute: China's mobile technology giant Huawei.
The meeting with business leaders at St. James's Palace brings together almost a dozen leading companies from the UK and the United States.
Jeremy Corbyn, the veteran socialist leader of Britain's opposition Labour Party, is due to speak at the protest.
Emily Thornberry, Labour's foreign affairs spokeswoman, says Trump is "a sexual predator" and a racist and does not deserve the honor of a state visit. I wish I was there when the queen gave him his gift. The two leaders have sharply differing views on issues including Iran, Brexit and Chinese telecoms firm Huawei.
But Trump said on Tuesday he wasn't contemplating any cutoff for Britain because he said he's sure the two sides will come to an agreement on Huawei.
Trump turned from pomp and ceremony to politics and business on Tuesday.
Britain is scheduled to leave the European Union on October 31, after pushing its original departure date back by several months because of a lack of agreement about what the deal should look like.